How to fix my project to be correctly opened by Blender versions newer than 2.82a?
The problem has to do with an empty that is in a collection attached to your Cantos object that cannot be opened to alter the contents (presumably because the empty is instancing it's own parent collection - there's your infinite loop). The solution, then, is to delete it, as I cannot see what function it serves other than causing problems (although you may have a different reason for needing it). However, the collection also contains a mesh that is the counterpart to the one on the other side. We'll deal with that in a minute.
First start by finding and deleting the offending collection:

You will see that this removes the clamp, and also forces the collection to dump it's contents, which in this case is the offending empty. Isolate and delete this too.

To put the clamp back (either in object mode, or edit mode - depending on what you want), I found duplicating and moving by -4.75 units on the X axis puts it right back in place.
Here's a picture from the file open in 2.83.

I'll also post the blend in case you need it quick.
File is here -